This invention relates in general to power amplifiers, and more particularly to a method and system for linearizing an amplified signal.
Power amplifier technologies are well known. However, power amplification of a signal can lead to undesirable distortion of the signal. Therefore, various method have been developed for correcting, or xe2x80x9clinearizing,xe2x80x9d the amplified signal. Linearizing is a process whereby nonlinear distortion of the signal caused by the amplifier is reduced. Specifically, an amplifier can introduce energy at unwanted frequencies in addition to increasing power of the desired frequencies. Through linearizing, the power level of the unwanted frequencies may be reduced.
Two common methods of linearizing are pre-distortion processing and feed-forward processing. Pre-distortion involves processing an input signal through a pre-distorter which, before amplification, adds distortion to the input signal corresponding to the distortion frequencies introduced by the main amplifier, but in the opposite phase. As the pre-distorted signal is then amplified by the main amplifier, the distortion components are at least partially cancelled out and the linear components remain. Pre-distortion processing is described in, for example, S. C. Cripps, RF Power Amplifiers for Wireless Communications, Boston: Artech House (1999).
Feed-forward processing was described in U.S. Pat. No. 1,686,792 issued to H. S. Black, and typically involves taking a sample of the main amplifier output, reducing the power of the amplifier output sample to the same level as the amplifier input, and then subtracting a sample of the amplifier input from the amplifier output sample, leaving a sample comprising an inverse (opposite phase) of the distortion generated by the amplifier. The inverse distortion sample is then amplified with a separate amplifier and fed into the main amplifier output, resulting in at least a partially linearized signal.
In some applications, current methods do not result in optimum levels of linearizing.
In accordance with one embodiment of the present invention, a method of processing an input signal to produce a corrected output signal includes generating a pre-distorted signal by distorting a digital input signal, the distortion based upon characteristics of a main amplifier, and correcting an output signal of the main amplifier to produce the corrected output signal. The output signal of the main amplifier is generated by amplifying the pre-distorted signal with the main amplifier. The correcting is based on a comparison of a signal indicative of the main amplifier output signal and a signal indicative of the digital input signal.
A technical advantage of certain embodiments of the present invention include increased overall linearizing. By effectively combining pre-distortion and feed-forward correction processes, the power of unwanted frequencies introduced by power amplification may in accordance with certain embodiments of the present invention be reduced by an amount greater than about 45 dB.
Certain embodiments may possess none, one, some, or all of these technical features and advantages and/or additional technical features and advantages. Other technical advantages will be readily apparent to one skilled in the art from the following figures, description, and claims.